

//给定两个整数数组 preorder 和 inorder ，其中 preorder 是二叉树的先序遍历， inorder 是同一棵树的中序遍历，请构造二叉树并
//返回其根节点。 
//
// 
//
// 示例 1: 
//
// 
//输入: preorder = [3,9,20,15,7], inorder = [9,3,15,20,7]
//输出: [3,9,20,null,null,15,7]
// 
//
// 示例 2: 
//
// 
//输入: preorder = [-1], inorder = [-1]
//输出: [-1]
// 
//
// 
//
// 提示: 
//
// 
// 1 <= preorder.length <= 3000 
// inorder.length == preorder.length 
// -3000 <= preorder[i], inorder[i] <= 3000 
// preorder 和 inorder 均 无重复 元素 
// inorder 均出现在 preorder 
// preorder 保证 为二叉树的前序遍历序列 
// inorder 保证 为二叉树的中序遍历序列 
// 
// Related Topics 树 数组 哈希表 分治 二叉树 
// 👍 1502 👎 0


/**
 * 105.从前序与中序遍历序列构造二叉树.construct-binary-tree-from-preorder-and-inorder-traversal
 *
 * @author orz
 * @since 2022-03-27 15:33:25
 **/

class Solution_105 {
    public static void main(String[] args) {
        Solution solution = new Solution_105().new Solution();
    }
    //leetcode submit region begin(Prohibit modification and deletion)

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     * int val;
     * TreeNode left;
     * TreeNode right;
     * TreeNode() {}
     * TreeNode(int val) { this.val = val; }
     * TreeNode(int val, TreeNode left, TreeNode right) {
     * this.val = val;
     * this.left = left;
     * this.right = right;
     * }
     * }
     */
    class Solution {
        public TreeNode buildTree(int[] preorder, int[] inorder) {
            return build(preorder, 0, preorder.length - 1, inorder, 0, inorder.length - 1);
        }

        private TreeNode build(int[] preorder, int preOrderStartIndex, int preOrderEndIndex,
                               int[] inorder, int inOrderStartIndex, int inOrderEndIndex) {
            if (preOrderStartIndex > preOrderEndIndex || inOrderStartIndex > inOrderEndIndex) {
                return null;
            }
            TreeNode node = new TreeNode(preorder[preOrderStartIndex]);
            int inOrderRootIndex = 0;
            for (int i = inOrderStartIndex; i <= inOrderEndIndex; i++) {
                if (inorder[i] == node.val) {
                    inOrderRootIndex = i;
                }
            }
            int preOrderLeftSize = inOrderRootIndex - inOrderStartIndex;
            ;
            node.left = build(preorder, preOrderStartIndex + 1, preOrderStartIndex + preOrderLeftSize,
                    inorder, inOrderStartIndex, inOrderRootIndex - 1);
            node.right = build(preorder, preOrderStartIndex + preOrderLeftSize + 1, preOrderEndIndex,
                    inorder, inOrderRootIndex + 1, inOrderEndIndex);
            return node;
        }
    }
//leetcode submit region end(Prohibit modification and deletion)

}